1. Field of the Invention
The present invention relates to a liquid crystal display device and a method for producing the same. More specifically, the present invention relates to a liquid crystal display device including a liquid crystal layer and a polymeric layer having birefringence in the same orientation state as the liquid crystal layer and at least partially surrounding the liquid crystal layer, and a method for producing such a liquid crystal display device.
2. Description of the Related Art
At present, liquid crystal display devices of a variety of display modes are used. For example, as liquid crystal display devices utilizing an electro-optic effect, those in a twisted nematic (TN) mode, those in a super-twisted nematic (STN) mode, which use nematic liquid crystal, those in an electrically controlled birefringence (ECB) mode, and those in a ferroelectric liquid crystal (FLC) mode have been put into practice. In these modes, polarization is utilized so that a polarizing plate is generally required. As a method for improving a viewing characteristic of a liquid crystal display device using such a polarizing plate, a method for producing a complex material of a liquid crystal material and a polymeric material (hereinafter known as photocurable resin) by causing phase separation of a mixture of the liquid crystal material and the polymeric material is disclosed in Japanese Laid-Open Patent Publication No. 5-27242. Such phase separation can be effected by selectively controlling the intensity of light using a photomask or the like, when the photocurable resin is photopolymerized.
On the other hand, for liquid crystal display devices utilizing scattering of liquid crystal without using a polarizing plate, devices utilizing a dynamic scattering (DS) effect and a phase change (PC) effect have come into existence.
Further, as scattering type liquid crystal display devices requiring neither a polarizing plate nor an alignment treatment, those utilizing the birefringence of liquid crystal so as to electrically control a transparent state and an opaque state have been proposed. In such a liquid crystal display device, the refractive index of the liquid crystal molecule with respect to ordinary light is basically matched with the refractive index of a supporting medium. More specifically, in the liquid crystal display device, the transparent state is shown when the liquid crystal molecules are uniformly aligned in the direction of the electric field by application of a voltage, and the opaque state is shown under application of no voltage because of light scattering caused by the turbulence of the liquid crystal molecules. Such a scattering type liquid crystal display device is produced, for example, by mixing a liquid crystal material and a polymeric material such as a photocurable resin or a thermosetting resin, and then curing the polymeric material to cause phase separation of the liquid crystal material and the polymeric material, so as to form a liquid crystal droplet in the polymeric material, as disclosed in Japanese National Publication No. 61-502128.
Generally, brightness and contrast of a device are important factors for a liquid crystal display device. The liquid crystal display device satisfying the brightness and the contrast at the same time is ideal. However, the brightness is usually more important for a reflective type liquid crystal display device, and the contrast is more important for a transmissive type liquid crystal display device. In particular, in the reflective type liquid crystal display device which utilizes phase separation between a liquid crystal material and a polymeric material, especially, in the liquid crystal display device which utilizes a polymer matrix type in which a liquid crystal layer is surrounded by a polymeric layer in order to improve impact resistance and pressure resistance, a problem that the liquid crystal display device as a whole becomes dark due to the polymeric layer has been caused.
In order to solve such a problem, in Japanese Patent Application No. 6-172740, "A liquid crystal display device and a method for producing the same", a liquid crystal display device in which molecules of the polymeric layer are aligned in the same manner as those of the liquid crystal layer is proposed. However, there is no suggestion about specific means for forming and fixing the polymeric layer by the phase separation between the polymeric material and the liquid crystal material while the polymeric material having anisotropy remains aligned. In such a liquid crystal display device, it is difficult to form the polymeric layer while the polymeric material remains aligned, whereby it is difficult to obtain a bright liquid crystal display device. Further, since such a polymeric material having anisotropy lacks rigidity, it is difficult to obtain a liquid crystal display device excellent in impact resistance and pressure resistance.
As described above, the liquid crystal display devices conventionally used have a variety of problems.